The present application relates to a display apparatus and an image pickup apparatus having the function of detecting a contact position of an object to be detected such as a finger or a pen.
Techniques for detecting a position where an object to be detected such as a finger or a pen is in contact with a display face of a display apparatus are known. Among them, a typified and popularized technique is a display apparatus having a touch panel. There are various types of touch panels, and a popularized one is a resistive type. In this type, a panel surface has a stack structure in which a very small spacer is sandwiched between glass and a film facing each other, and a transparent electrode grating is provided for each of the facing surfaces of the glass and the film. When the surface of the film is touched with a finger or a pen, the film is deformed, the transparent electrode on the film surface and the transparent electrode on the glass surface come into contact with each other, and current flows. By measuring a voltage dividing ratio of resistance of the transparent electrodes on the glass surface and the film surface, the position of the finger or the pen is detected. Therefore, by using such a touch panel, the user is able to operate intuitively.
In a touch panel of this type, however, a panel has to be pressed with pressure by a finger or pen to make position information detected. There is consequently a disadvantage such that if the press force is weak, the position information may not be detected correctly.
To address the disadvantage, recently, various techniques capable of detecting the position of an object to be detected without providing such a touch panel on the display surface are proposed. For example, Japanese Unexamined Patent Application Publication No. 2004-318819 (patent document 1) proposes a liquid crystal display in which light reception elements are disposed adjacent to a display pixel and, in a period in which display (light emission) stops, light reception is performed by the light reception elements. When such a display apparatus is used, the position of an object to be detected may be detected on the basis of a captured image. Therefore, by using such a display apparatus, the position of an object to be detected may be detected with a simple configuration without providing a part such as a touch panel on the display surface.
However, at the time of capturing a video image to be detected or the like in such a display apparatus, the intensity of light received is influenced by the ambient environment (brightness). In particular, in the case where a display apparatus whose ambient environment easily changes such as a portable electronic device is provided with the function of detecting the position of an object to be detected, light receiving conditions in a state where the environment is dark and those in a state where the environment is light are largely different from each other. It is difficult to detect the position of an object to be detected in uniform light reception conditions.
For example, the patent document 1 proposes a measure of detecting a change with time of black and white of data captured when an object to be detected approaches or comes into contact with a display surface in a liquid crystal display and specifying the position of the object to be detected in consideration of the ambient brightness. The patent document 1 also proposes another measure. In the case of making a fine-tipped object such as a pen approach or come into contact with the display surface, in consideration that a change with time of black and white of captured data does not become large, the tip of the pen is made of a soft material. When the pen comes into contact with the display surface, the tip of the pen is deformed and the contact area changes.
However, in the measure of the patent document 1, at the time of writing a character or a picture by touching the display surface with a fine-tipped object such as a pen, a special pen as described above has to be used, and there is a disadvantage that simplicity deteriorates.